/*
 * Alloy Analyzer
 * Copyright (c) 2002 Massachusetts Institute of Technology
 *
 * The Alloy Analyzer is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * The Alloy Analyzer is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with the Alloy Analyzer; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

package alloy.semantic;

import alloy.ast.ASTDepthFirstReturnVisitor;
import alloy.ast.InvocationExpr;
import alloy.util.Dbg;
import alloy.util.Msg;

/**
 * <p>
 * Alloy Analyzer<br>
 * Copyright (c) 2001<br>
 * Massachusetts Institute of Technology<br>
 * <p>
 * Class: InvocationErrorVisitor<br>
 * owner: brianlin<br>
 * Interface status: unstable<br>
 * Implementation status: unstable<br>
 * <p>
 * A visitor that signals an error if it encounters an invocation.
 * This visitor should be used on expressions in field declarations
 * and function argument declarations, where invocations cannot
 * appear.
 */

public class InvocationErrorVisitor extends ASTDepthFirstReturnVisitor {

    /**
     * Visit an invocation.  Signal an error since
     * an invocation shouldn't appear in this context.
     * @param invocationExpr_ the invalid invocation
     * @return <code>null</code> to signal the error
     */
    public Object visit(InvocationExpr invocationExpr_) {
        Dbg.user(new Msg("an invocation cannot appear in this context", invocationExpr_));
        return null;
    }
}
    

